1. Field of the Invention
The present invention relates to an apparatus for analysis and evaluation of characteristics of series-connected solar battery cells. The apparatus analyzes and evaluates an analysis model of solar battery cells produced by a finite element method to thereby contribute to production of a solar battery having a series connection structure.
2. Description of the Background Art
A solar battery has a transparent electrode of indium oxide (ITO) or the like on a light incidence side, and a rear electrode of a metal on a light reflection side. The solar battery is formed so that light is guided from the transparent electrode side to a semiconductor film for photoelectric conversion, and that electric power due to photoelectric conversion is obtained from the rear electrode side (see JP-A-2-98975 (FIG. 5)). In this case, it is general that efficiency becomes lower than characteristic obtained by measurement of a small-area cell as a single test piece because of a voltage drop caused by wiring resistance of respective parts including the transparent electrode and the rear electrode. In a structure in which series connection of unit cells is performed based on a pattern formed in the same manner as in production of an electronic device such as an integrated circuit, it is therefore essential to grasp the degree of lowering of efficiency in advance to design the pattern. Particularly when there are a back electrode and through-holes for wiring in addition to the transparent electrode and the rear electrode as in an SCAF (Series Connection through Apertures formed on Film) structure shown in “Current Status and Future Trends of Amorphous Silicon Solar Cells” by Masahiro Sakurai and Toshiaki Sakai in Fuji Electric Journal Vol. 78, No. 6, 2005, pp. 29-33 (pp. 30, FIG. 2), it is important to grasp the degree of lowering of efficiency in advance before product planning because the degree of freedom in designing the pattern becomes high.
On this occasion, a simplified network model has been heretofore constructed uniquely in accordance with the pattern, and maximum electric power, fill factor (FF), etc. have been obtained by simple calculation on the network model.
In the simplified network model according to the background art, calculation is however performed based on resistors substituted for the wiring, the through-holes, etc. Accordingly, there is a problem that it is difficult to accurately calculate the influence of through-hole shape, arrangement of the through-holes, details of electrode shape, etc. on characteristic. Moreover, if shapes of the through-holes and electrodes are changed, there is a problem that it is more difficult to accurately calculate the influence on characteristic because a lot of new assumptions are placed for simplified calculation in addition to the necessity to reconstruct the network model.
On the other hand, wiring resistance automatic analysis software etc. cooperating with a mask CAD or the like to consider the pattern accurately is available on the market in the field of design of electronic devices such as integrated circuits. However, the wiring resistance automatic analysis software in the field of design of electronic devices cannot be applied to analysis of characteristic of a solar battery because modeling of a battery forming the backbone of power generation in a solar battery or generation of a current on a surface from a wiring pattern per se is not assumed.
On the other hand, if a series-connection structure shape model created by general-purpose finite element method software available on the market is used for current analysis, it is also possible to calculate a potential distribution (voltage drop) in consideration of detailed shape. However, (A) it is necessary to reconstruct the series-connection structure model whenever the pattern is changed, similarly to the aforementioned network model. Moreover, those who have no technical skill cannot use the software easily on the site of pattern designing. In addition, (B) even when a calculation result of the potential distribution (voltage drop) due to wiring resistance is obtained based on a constant current set in the electrode portion of a series-connection structure shape model constructed by use of the finite element method software, the potential distribution per se shows that the generated current is not constant (smaller than the set value), and the calculation result provides nothing more than first-order approximation.
On the contrary, it may be conceived that convergence calculation is performed by use of finite element method software. However, it is necessary to repeat calculation by tens to hundreds of times after modeling all series-connected cells arranged as a large number of cells, for example, as shown in FIG. 5A. This is not realistic in view of analysis time. It may be therefore conceived that analysis is tried on one unit cell extracted and modeled from the large number of series-connection structures arranged. In this case, it is however necessary to define a boundary condition in each cut portion. In the case of series-connected cells as shown in FIG. 5A, anyplace where wiring per se is cut is the place where a current flows. Accordingly, the measures to define the current or potential to be originally analyzed as a boundary condition are self-contradictory.